Transcription termination on the coliphage lambda chromosome is suppressed by the viral N protein. Host mutations which block N action (nus, groN) also affect transcription termination on the bacterial chromosome. We find that nusB mutants are defective in transcribing ribosomal RNA; we are selecting additional E. coli mutants with this defect. We have designed a novel lambda vector to perform this selection, and to verify that transcription termination is affected in these mutants. Other E. coli mutations that alter transcription termination have been isolated as suppressors of the nusAl phenotype. One such suppressor appears to lie in gene "u", which encodes a 21 kd protein and is located in a cluster of genes involved in mRNA translation. We wish to determine the nature of the "u" product, and to ask if it serves as a link between transcription and translation. Bacteriophage lambda does not propagate on E. coli lysogenic for phage HK022. This exclusion is due to a HK022 prophage function, Nun, which acts as a new transcription termination factor. Nun interacts with Nus factors to provoke premature termination at the lambda nut sites.